The present invention relates generally to roof paving systems, and more particularly it relates to an improved protected-membrane roof and deck paver system which is aerodynamically stable and to a ballast block for use in such system.
Recent developments in roof paver technology have resulted in the introduction of single-ply protected-membrane roof systems which are especially suitable for low-sloped roofs and decks. They usually include a single-ply water-impermeable membrane, with or without thermal insulation layers, held in place and protected from the elements by ballast systems of various types and configurations. Basic systems include loose-laid well-rounded stones such as river gravel, standard paving blocks, composite tongue-and-groove board, and lightweight interlocking ballast blocks. In general, ballast systems are often the preferred system of choice in areas where exposure to high wind conditions may be anticipated because they are capable of withstanding greater wind velocities than conventional built-up roofing systems. Studies have also shown that ballast systems which utilize interlocking blocks perform even better under adverse (strong) wind conditions than non-interlocking ballast systems.
The interlocking blocks are usually extruded or precast concrete of flat rectangular shape laid over a roof membrane in a contiguous grid pattern. However, even this construction does not assure dislodgement of the ballast blocks under certain weather conditions. High velocity winds, such as of hurricane-force, passing over irregular or critical roof locations may induce an aerodynamic pressure differential across the blocks to lift them out of place. Instead of simply making ballast blocks heavier and the roof supports stronger, various designs have evolved for resisting the lifting force, such as the aforementioned lightweight ballast blocks secured to each other by interlocking edges. However, despite these design efforts, the net upward aerodynamic loading acting on the ballast blocks may lift them into the airstream like flying missiles and endanger people and other structures in the vicinity as well as expose the underlying roof membrane and substructure to damage.